Effect of palm oil on oxidative stress-induced hypertension in Sprague-Dawley rats

Background: Oxidative stress, associated with increased plasma isoprostane (ISO) and reductions in plasma glutathione (GSH), has been shown to cause severe hypertension in normal rats. Palm oil (PO), with an unsaturated-to-saturated fatty acid ratio close to one and rich in antioxidant vitamins, has been investigated for its beneficial effects on arterial thrombosis and atherosclerosis. In this study, the effect of PO on oxidative stress induced by inhibition of GSH synthesis (using buthionine sulfoximine [BSO]) was examined. Methods: Sprague-Dawley rats were separated into two groups and received either natural vitamin-rich PO (Carotino, 5 g/kg daily) or water by gavage. After 4 weeks, they were further divided between receiving either BSO (30 mmol/L/day in the drinking water) or drug-free water for an additional week. Mean arterial pressure (MAP), heart rate (HR), and body weight (BW) were measured before and weekly during the experiment. The levels of plasma ISO, nitric oxide (NO), prostacyclin (PGI(2)), and thromboxane A(2) (TXA(2)) were determined by enzyme immunoassay, and plasma, heart, and kidney GSH by high-performance liquid chromatography. Results: The PO reduced the age-dependent increase in MAP, and the pressor response to BSO, without changing the HR or BW compared to the BSO and control groups. It also elevated PGI(2), NO, and aortic cGMP, but decreased TXA(2) and aortic cAMP. In addition, the BSO-induced increase in ISO and TXA(2), and the reduction in kidney GSH were attenuated by PO. However, the PO effect on NO, PGI(2), cGMP, and TXA(2) was partly counteracted by BSO. Conclusions: Palm oil reduces BSO-induced oxidative stress and attenuates hypertension by mechanisms involving changes in endothelium-derived factors.